Process for graft copolymerization on surfaces of preformed substrates to modify surface properties

ABSTRACT

A process for modifying the surface characteristics of a preformed polymeric substrate to impart hydrophilicity, hydrophobicity or other desired properties thereto comprises peroxidizing and hydroperoxidizing the surface of said preformed substrate using ozone, directing the subsequent graft polymerization of selected ethylenically unsaturated monomers essentially solely to the surface of said substrate to achieve the desired alteration of substrate surface characteristics while maintaining substrate structural integrity. Substrates so modified are useful in biomedical devices, semipermeable membranes, films, fibers and especially contact lenses.

This invention is to a process for modifying the surfaces of preformedpolymer substrates by the controlled graft polymerization thereon ofselected ethylenically unsaturated monomers and to products made by saidprocess.

BACKGROUND OF THE INVENTION

Graft polymerization per se has long been known in the art with manygraft copolymers such as ABS (acrylonitrile butadiene/styrene) resinsachieving considerable commercial success.

It has also been known in the art that various vinylic monomers can begraft polymerized onto polymer substrates which have been first treatedwith ionizing radiation in the presence of oxygen or with ozone to formperoxy groups on the surface of said substrate. U.S. Pat. Nos. 3,008,920and 3,070,573 teach the grafting of selected monomers onto ozonatedpolymer substrates.

While such a process would in theory seem to be a panacean method tomodify at will the surface characteristics of any polymer substrate,such is not the case as is seen in the teachings of U.S. Pat. Nos.4,311,573 and 4,589,964.

The objective of such graft polymerization is to modify the surface ofthe polymer substrate without causing major changes in the physicalcharacteristics of the substrate as a whole.

Problems have arisen when such a graft polymerization process is carriedout. One serious complication involves graft polymerization of thevinylic monomer onto the substrate as desired, but with the simultaneousand undesired homopolymerization of the vinylic monomer. This problemcan be minimized by carrying out the graft polymerization process in thepresence of a metal redox system using a variable valence metal ion inthe reduced state to convert any hydroxyl free radical present tohydroxyl ion and thus minimize the simultaneous homopolymerizationproblem. See U.S. Pat. Nos. 3,008,920, 4,311,573 and 4,589,964.

U.S. Pat. Nos. 4,311,573 and 4,589,964 teach that another problemencountered in the surface grafting of a preformed polymeric substrateconcerns depth and density control of the graft. If the bulk propertiesof the substrate are to be retained, then the graft depth should be nogreater than necessary to modify the surface characteristics of thearticle. Grafts of excessive depth, grafts of insufficient density toachieve the desired property modification and the swelling anddegradation of the substrate article during the process are seriousproblems plaguing this panacean process.

U.S. Pat. Nos. 4,311,573 and 4,589,964 teach a method aimed atinhibiting homopolymerization, at controlling graft depth and ataccelerating graft polymerization to increase graft density, namely bycarrying out the graft polymerization in the presence of a variablemetal ion (ferrous) and a complexing agent (squaric acid) to controlmobility of said ions.

The instant process is an improvement over the process of U.S. Pat. Nos.4,311,573 and 4,589,964 by controlling the depth of the graftpolymerization on the substrate by saturating the polymer substrate onwhich grafting is to occur by a liquid in which the ethylenicallyunsaturated monomer system is insoluble. No complexing agent such assquaric acid is required in the instant process.

OBJECTS OF THE INVENTION

One object of this invention is to provide a facile process formodifying the surface characteristics of a preformed polymeric substrateto impart desired properties thereto.

Another object of this invention is to prepare contact lenses,biomedical devices or other useful materials by the process of thisinvention.

DETAILED DISCLOSURE

The instant invention is to a process for modifying the surfacecharacteristics of a preformed polymer substrate to imparthydrophilicity, hydrophobicity or other desired properties thereto bygraft polymerization on said substrate, having peroxy and hydroperoxygroups on said polymer, of an ethylenically unsaturated monomer, whereinthe improvement comprises

carrying out the graft polymerization on the polymer substrate which issaturated or swollen with a liquid, before or after ozonation, in whichthe ethylenically unsaturated monomer is insoluble to preventpenetration of said monomer into the interior of the substrate and todirect graft polymerization of said monomer to the surface of thesubstrate.

In preliminary steps in the instant process, the polymer substrate canbe saturated or swollen with the liquid either before or after theozonization step to form the peroxy and hydroperoxy groups on saidsubstrate is performed.

Another embodiment of the instant invention is to a process formodifying the surface characteristics of a preformed polymer substrateto impart hydrophilicity, hydrophobicity or other desired propertiesthereto by graft polymerization on said substrate, having peroxy andhydroperoxy groups on said polymer, of an ethylenically unsaturatedmonomer, which comprises

contacting the polymer substrate with a solution which is or contains achain transfer agent, preferably a primary or secondary C₁ -C₄ -alkanol,to saturate or swell said polymer, said solution being insoluble in theperhalogenated liquid medium used subsequently during the ozonationstep, to limit subsequent hydroperoxidation and peroxidation to thesurface of said polymer,

ozonating the saturated or swollen polymer with ozone dissolved in aperhalogenated liquid medium insoluble in the solution containing thechain transfer agent, and

then graft polymerizing an ethylenically unsaturated monomer ontoessentially only the surface of the polymer substrate.

The substrate after exposure to ozone will have on its surface bothperoxy (--O--O--) and hydroperoxy (--OOH) groups. Upon thermal orotherwise induced decomposition, the peroxy groups cleave into twoactive free radicals attached to the surface of the polymeric substrateoffering sites on the surface to initiate graft polymerization with theethylenically unsaturated monomer.

On the other hand upon thermal or otherwise induced decomposition, thehydroperoxy groups also cleave into two active free radicals. One isattached to the polymer surface and is capable of initiating graftpolymerization thereon while the other is a free hydroxyl radical notattached to the surface. This latter free radical is available toinitiate homopolymerization of the monomer unless suchhomopolymerization is inhibited or suppressed.

U.S. Pat. Nos. 3,008,920 and 4,589,964 teach that an effectivehomopolymerization-inhibiting agent is the cuprous, ferrous or othervariable valence metal ion such as those of cobalt, manganese,molybdenum, tin, indium, cerium, chromium, thallium and vanadium. Apreferred metal salt providing such metal ion is ferrous ammoniumsulfate although other ferrous salts such as ferrous sulfate, ferrouschloride, ferrous iodide and ferrous bromide can be used as well.

These reduced valence (-ous) salts react with the hydroxyl free radicalin a redox system to produce the hydroxyl radical and the oxidized (-ic)salt. With the concentration of hydroxyl free radical thus minimized oreliminated, there is no initiator for the homopolymerization which isnow effectively suppressed.

Since in general the presence of homopolymer unattached to the surfaceof the substrate is undesirable leading to high extractables andunstable surface characteristics, a homopolymerization-inhibiting agentis usually present in the graft polymerization step of the instantprocess.

However, there is one variation of the instant process where crosslinkedhomopolymerization is an important aspect of the instant inventionproviding a method for encapsulating a substrate by an envelope of thehomopolymer. In this variation of the instant process, the ethylenicallyunsaturated monomer is allowed to be initiated, with a reduced ferrousion concentration, both by the active free radicals attached to thesurface of the substrate as well as by the free active hydroxyl freeradical present in the system. No or littlehomopolymerization-inhibiting agent is present in this variation of theinstant process. The entire hydrogel polymer network is covalently boundin a three-dimensional structure through the presence of a crosslinkingagent.

The encapsulation of materials with a protective coating which can beremoved in a controlled fashion as by weathering or by exposure to aperiod in the soil is a utility for products made by this processvariation. Protective coatings for seeds is contemplated.

It is known that the use of variable valence metal ions, for exampleferrous or cuprous, can inhibit homopolymerization during graftpolymerization of a substrate containing hydroperoxy groups.

However, while the ferrous ion inhibits homopolymerization, there is alimitation in its use since such ions subsequently penetrate into thepolymeric substrate allowing for the desired graft polymerization tooccur at an undesired spot, namely in the interior of the substrate.

The effect of this graft polymerization at the wrong place is adistortion of the substrate with a concomitant loss in physicalproperties and dimensional stability and integrity. Such distortion isgenerally undesirable for obvious reasons and in the contact lens fieldis intolerable.

Another aspect of the instant invention is the ability to create a softpolymer skirt around the periphery of a rigid polymer contact lens.Current technology to prepare such modified lenses is complex, laboriousand prohibitively uneconomic.

The instant process, however, affords a facile route for the productionof such modified lenses. Following the ozonation of the rigid polymericlens substrate to form peroxy and hydroperoxy groups thereon, theozonated lens is placed in a mold where the center of the ozonated lensis covered and where the periphery of said ozonated lens is exposed toan aqueous grafting solution containing a hydrophilic monomer andcrosslinking agent. The grafting solution will contain an appropriatemixture of hydrophilic and crosslinking monomers to impart the desiredproperties required for the soft polymer skirt of the contact lens togive the rigid contact lens greatly improved eye comfort and otherancillary benefits not normally associated with rigid contact lenses.

The filled mold containing the appropriate grafting monomers is exposedto UV light. This irradiation decomposes the peroxy and hydroperoxygroups present on the peripheral portion of the ozonated lens toinitiate graft and crosslinked copolymerization of the monomer mixturein the mold to form a soft polymer skirt of desired properties firmlybonded via the grafts to the periphery of the rigid contact lens.

The preformed polymeric substrate which can be used in this process canbe any fabricated polymeric product such as a film, fiber, pellicle,device or object including contact lenses whose surface characteristicsare in need of modifying in some fashion to impart hydrophilicity,hydrophobicity, dyeability (tinting), opacity, diffraction differences,wettability, bonding characteristics, oxygen permeability, bactericidalproperties, lubricity, and the like.

The only requirement is that the polymer from which the fabricatedproduct is made must itself have a hydrocarbon group somewhere in itsstructure making it amenable to peroxidation and hydroperoxidation whenexposed to ozone to form peroxy and hydroperoxy groups on the preformedpolymeric substrate surface.

Polymeric materials useful in this instant invention include inter aliapolyolefins, polyesters, polyamides, cellulosics, polyurethanes,non-silicone hydrogels, hydrophilic polysiloxanes, hydrophobicpolysiloxanes, polymers containing poly(alkylene oxide) units,polycarbonates, silicone rubber, natural and synthetic rubber, epoxyresins, polyvinyl chloride, polystyrene, poly(methyl methacrylate) andcopolymers and the like.

The peroxy and hydroperoxy groups are conveniently introduced onto thesurface of the preformed polymeric substrate by subjecting saidsubstrate to ozone (03). This can be done by appropriately suspending,placing or otherwise fixing the preformed substrate in a chamber orvessel so that the surfaces to be modified will be intimately contactedwith ozone in a gaseous carrier such as ozonated air or ozonated oxygenor with ozone dissolved in a perhalogenated solvent for a period of timesufficient to result in the requisite uptake of ozone onto the polymersurface to form the desired peroxy and hydroperoxy groups. Generallythis time required is less than one hour, usually about 30 minutes.

The reaction temperature is generally not critical, and the reaction canbe conducted over a wide temperature range from between 0° and 100° C.For convenience ambient temperatures are preferred.

In order to facilitate the reaction between the polymer substrate andozone to form the hydroperoxidized substrate, it is preferable for thereaction to be carried out in the presence of a small amount ofmoisture. Indeed, with hydrogel materials the polymeric substrate can besaturated with water before ozonization is carried out.

Ozone can be conveniently prepared in admixture with a carrier gas bypassing an oxygen containing gas, such as air or pure oxygen, through astandard ozone generator. In the case of air, about 2% ozone by weightis generally produced. In the case of pure oxygen, about 4% ozone byweight is characteristically produced.

The ozone prepared by the ozone generator can also be dissolved in aperhalogenated solvent such as inter alia carbon tetrachloride,1,1,2-trichloro-1,2,2-trifluoroethane, octafluorocyclobutane,perfluorohexane, perfluoroheptane, perfluoro-(1,3-dimethylcyclohexane),perfluorocyclohexane, 1,1,1-trichloro-2,2,2-trifluoroethane,1,1,1,2-tetrachloro2,2-difluoroethane and1,1,2,2-tetrachloro-1,2-difluoroethane. Preferably carbon tetrachloride,perfluoro-(1,3-dimethylcyclohexane),1,1,2-trichloro-1,2,2-trifluoroethane or perfluorohexane is theperhalogenated solvent of choice.

In an alternative embodiment of the instant invention, the preformedpolymer substrate is first saturated or swollen with a solution which isor contains a chain transfer agent before the subsequent ozonizationstep is carried using ozone dissolved in a perhalogenated solvent. Thesolution containing the chain transfer agent is insoluble in the liquidmedium containing the ozone. The perhalogenated solvents are thosementioned above particularly perfluoro-(1,3-dimethylcyclohexane).

The chain transfer agent is preferably a primary or secondary alkanol of1 to 4 carbon atoms such as methanol, ethanol, n-propanol, isopropanol,n-butanol, sec-butyl alcohol or isobutyl alcohol. The solutioncontaining the chain transfer agent can also contain water or a tertiarylower alkanol, such as tert-butyl alcohol, to assist in solubilizing thechain transfer agent.

While other materials such as mercaptans are also effective chaintransfer agents, mercaptans are precluded from serious consideration forthat purpose for aesthetic reasons (poor odor properties).

Isopropanol is a particularly preferred chain transfer agent in theinstant process.

Two benefits accrue from this alternative embodiment of the instantinvention especially in the case of substrates which are hydrogels.These are:

First, the ozonization occurs on the polymer substrate in the swollen orextended state. The subsequent graft copolymerization can then occurwith the substrate already in the normal physical state and size inwhich the end-use product, i.e. biomedical device, contact lens, etc,will be used minimizing structural and dimensional changes which mightotherwise occur during use.

Second, the primary or secondary alcohol acts as a chain transfer agent.The presence of such material inside the swollen polymer substrate helpsprevent any subsequent graft polymerization from occurring in theinterior of the polymer substrate later in the instant process bylimiting the peroxidation and hydroperoxidation to the surface of thesubstrate.

Another aspect of the instant invention is the ozonation of polysiloxanepolymer substrates, particularly contact lenses, in the presence of aperhalogenated hydrocarbon liquid, particularly1,1,2-trichloro-1,2,2trifluoroethane. Polysiloxane contact lenses havehigh surface tack making them stick together when ozonated in gaseous orin aqueous media causing irreparable damage to said lenses when theirseparation is attempted.

The polysiloxane swells in the perhalogenated hydrocarbon liquid andozone is highly soluble in said liquid leading to a large (up to 13times) increase in peroxy and hydroperoxy sites, compared to ozonationin water, on the surface of the polysiloxane lenses suitable for latergraft polymerization.

Following the exposure of the preformed polymeric substrate to ozone insome gaseous or liquid medium, the ozonated substrate is allowed to airdry at ambient temperature to eliminate any residual ozone. Whileozonation has occurred primarily at sites on the exposed surfaces, someperoxidized and hydroperoxidized groups may also be present in anyadventitious internal interstices or recesses available to the ozone.

Since the ozonated substrate contains peroxy and hydroperoxy groupswhich are unstable when raised to elevated temperatures, the ozonatedsubstrate can be kept for long periods of time (several months) a lowtemperature (0° to 20° C.) in an atmosphere of nitrogen without loss ofthe peroxy and hydroperoxy groups.

In order to prevent undesired changes in overall polymer propertiesinvolving the basic integrity of the substrate itself, it is desirableto prevent or at least to minimize any subsequent grafting of themodifying monomer by graft polymerization anywhere on the preformedpolymer substrate except on the surface of said substrate.

To prevent the penetration of the grafting monomer into the polymersubstrate to any appreciable depth, the ozonated substrate after airdrying to remove residual ozone may be treated by several route beforegraft polymerization is attempted. In each case, the ozonated substrateis purged with nitrogen so that subsequent graft polymerization is notimpeded.

If penetration of the ozonated substrate is not expected to be a problembecause of the nature of the substrate of the vinyl monomer being usedin the graft polymerization for reasons of size, molecular weight,polarity etc, the air-dried, nitrogen-purged ozonated substrate can beused directly for the graft polymerization step without undue fear ofappreciable internal penetration of the graft monomer into thesubstrate.

In those cases where such penetration of the vinyl graft monomer wouldpose a potential problem, the air-dried ozonated substrate is purgedwith nitrogen and then saturated with a liquid in order to fill up theinternal interstices and recesses of the substrate. The liquid is chosenso that the graft monomer system is essentially insoluble therein. Thegraft monomer is thus essentially precluded from grafting on thesubstrate anywhere except on the surface of said substrate. Thisprovides a facile method to direct the grafting to the precise areaswhere modification of the substrate surface is desired while leavinguntouched the gross physical properties of the substrate.

Depending on the solubility properties of the graft monomer system beingused, the saturating liquid can be water, an organic hydrocarbon, aperhalogenated hydrocarbon or mixture of liquids.

The organic hydrocarbon liquids useful for saturating the ozonatedsubstrate are inert to vinyl polymerization and include aliphatic,cycloaliphatic and aromatic hydrocarbons such as inter alia hexane,heptane, cyclohexane, toluene and xylene.

The perhalogenated hydrocarbons useful for saturating the ozonatedsubstrate are inter alia carbon tetrachloride,1,1,2-trichloro-1,2,2-trifluoroethane, octafluorocyclobutane,perfluorohexane, perfluoroheptane, perfluorocyclohexane,1,1,1-trichloro-2,2,2-trifluoroethane,perfluoro-(1,3-dimethylcyclohexane),1,1,1,2-tetrachloro-2,2-difluoroethane and1,1,2,2-tetrachloro-1,2-difluoroethane.

Generally, it requires only a relatively small amount of material (byweight) to be actually grafted onto the surface of a polymer substrateto achieve the desired modification in the substrate surface properties.

The graft polymerization is generally carried out using an aqueoussolution of an ethylenically unsaturated monomer or mixture of monomerscapable of undergoing graft addition polymerization onto the surface ofthe substrate. In those cases where the monomer is not appreciablysoluble in water, a cosolvent, preferably tert-butyl alcohol, is used toenhance the solubility of the monomer in the aqueous graftpolymerization system.

If desired, the graft polymerization mixture may contain a catalyticamount of a conventional catalyst characteristically employed inpolymerizing vinylic compounds, preferably a free radical catalyst. Ofparticular interest are the conventional peroxide and azo catalysts suchas hydrogen peroxide, benzoyl peroxide, tert-butyl peroctoate orazobis(isobutyronitrile). In many cases, an added initiator is notneeded due to the innate activity of the ozonated substrate with itsperoxy and hydroperoxy groups.

Additionally where indicated, the graft polymerization can be carriedout in the presence of actinic radiation with or without the presence ofa photoinitiator.

The choice of the monomer or monomers depends on the nature of thesubstrate and on the particular surface modification desired. Thus themonomers may be hydrophilic, hydrophobic, crosslinking agents, dyesites,bactericidal or with any of a wide gamut of properties as required toachieve the modification desired.

Suitable hydrophilic monomers include generally water solubleconventional vinyl monomers such as:

acrylates and methacrylates of the general structure ##STR1## where R₂is hydrogen or methyl and R₃ is hydrogen or is an aliphatic hydrocarbongroup of up to about 10 carbon atoms substituted by one or more watersolubilizing groups such as carboxy, hydroxy, amino, lower alkylamino,lower dialkylamino, a polyethylene oxide group with from 2 to about 100repeating units, or substituted by one or more sulfate, phosphate,sulfonate, phosphonate, carboxamido, sulfonamido or phosphonamidogroups, or mixtures thereof;

acrylamides and methacrylamides of the formula ##STR2## where R₂ and R₃are as defined above;

acrylamides and methacrylamides of the formula ##STR3## where R₄ islower alkyl of 1 to 3 carbon atoms and R₂ is as defined above;

maleates and fumarates of the formula

    R.sub.3 OOCCH═CHCOOR.sub.3

wherein R₃ is as defined above;

vinyl ethers of the formula

    H.sub.2 C═CH--O--R.sub.3

where R₃ is as defined above;

aliphatic vinyl compounds of the formula

    R.sub.2 CH═CHR.sub.3

where R₂ is as defined above and R₃ is as defined above with the provisothat R₃ is other than hydrogen; and

vinyl substituted heterocycles, such as vinyl pyridines, piperidines andimidazoles and N-vinyl lactams, such as N-vinyl-2-pyrrolidone.

Included among the useful water soluble monomers are:

2-hydroxyethyl-; 2- and 3-hydroxypropyl-; 2,3-dihydroxypropyl-;polyethoxyethyl-; and polyethoxypropylacrylates, methacrylates,acrylamides and methacrylamides;

acrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide,N,N-dimethylacrylamide, N,N-dimethylmethacrylamide;

N,N-dimethyl- and N,N-diethyl-aminoethyl acrylate and methacrylate andthe corresponding acrylamides and methacrylamides;

2- and 4-vinylpyridine; 4- and 2-methyl-5-vinylpyridine;N-methyl-4-vinylpiperidine; 2-methyl-1-vinylimidazole;N,N-dimethylallylamine; dimethylaminoethyl vinyl ether;N-vinylpyrrolidone; acrylic and methacrylic acid; itaconic, crotonic,fumaric and maleic acids and the lower hydroxyalkyl mono and diestersthereof, such as the 2-hydroxyethyl fumarate and maleate, sodiumacrylate and methacrylate; maleic anhydride;2-methacryloyloxyethylsulfonic acid and allylsulfonic acid.

Preferred water soluble monomers include 2-hydroxyethyl methacrylate,N,N-dimethylacrylamide, acrylic acid and methacrylic acid, and mostpreferably 2-hydroxyethyl methacrylate.

Suitable hydrophobic copolymerizable monomers include water insolubleconventional vinyl monomers such as:

acrylates and methacrylates of the general formula ##STR4## where R₂ isas defined above and R₅ is a straight chain or branched aliphatic,cycloaliphatic or aromatic group having up to 20 carbon atoms which isunsubstituted or substituted by one or more alkoxy, alkanoyloxy or alkylof up to 12 carbon atoms, or by halo, especially chloro or preferablyfluoro, or C₃ -C₅ polyalkyleneoxy of 2 to about 100 units;

acrylamides and methacylamides of the general formula ##STR5## where R₂and R₅ are defined above;

vinyl ethers of the formula

    H.sub.2 C═CH--O--R.sub.5

where R₅ is as defined above;

vinyl esters of the formula

    H.sub.2 C═CH--OCO--R.sub.5

where R₅ is as defined above;

maleates and fumarates of the formula

    R.sub.5 OOC--HC═CH--COOR.sub.5

where R₅ is as defined above;

and vinylic substituted hydrocarbons of the formula

    R.sub.2 CH═CHR.sub.5

where R₂ and R₅ are as defined above.

Useful hydrophobic monomers include, for example:

methyl, ethyl, propyl, isopropyl, butyl, ethoxyethyl, methoxyethyl,ethoxypropyl, phenyl, benzyl, cyclohexyl, hexafluoroisopropyl orn-octyl-acrylates and -methacrylates as well as the correspondingacrylamides and methacrylamides;

dimethyl fumarate, dimethyl maleate, diethyl fumarate, methyl vinylether, ethoxyethyl vinyl ether, vinyl acetate, vinyl propionate, vinylbenzoate, acrylonitrile, styrene, alpha-methylstyrene, 1-hexene, vinylchloride, vinyl methyl ketone, vinyl stearate, 2-hexene and 2-ethylhexylmethacrylate.

Suitable crosslinking agents are diolefinic monomers such as:

allyl acrylate and methacrylate; alkylene glycol and polyalkylene glycoldi-acrylates and -methacrylates, such as ethylene glycol dimethacrylate,and propylene glycol dimethacrylate; trimethylolpropane triacrylate;pentaerythritol tetraacrylate, divinylbenzene; divinyl ether; divinylsulfone;

bisphenol A diacrylate or methacrylate; methylene-bisacrylamide; diallylphthalate; triallyl melamine; and hexamethylene diacrylate anddimethacrylate.

The following examples are presented for the purpose of illustrationonly and are not to be construed to limit the nature or scope of theinstant invention in any manner whatsoever.

EFFECT OF OZONATION IN A HALOCARBON ON HYDROPEROXIDE YIELD AND DEGREE OFGRAFTING EXAMPLE 1 Ozonation of Polysiloxane Hydroperoxide Yield

To determine the relative ozonation rates of polysiloxane film in wateras compared to perhalogenated hydrocarbons, separate samples of the samepolysiloxane film are placed in water and in1,1,2-trichloro-1,2,2-trifluoroethane (Freon TF or 113) into whichozone, prepared in a standard ozone generator, is passed at roomtemperature for 30 minutes. The solubility of ozone in water is 4.5 ppmwhile in Freon TF or 113 is 491 ppm.

The samples of polysiloxane films in the water system clump togethervery quickly. Analysis of hydroperoxide content (iodometric titrationmethod) in said films shows 0.924 mg/g or a 0.09% hydroperoxide content.

The samples of polysiloxane film ozonated in the Freon TF or 113 systemstay separate and analysis of hydroperoxide content on said films shows12 mg/g or a 1.2% hydroperoxide content.

Clearly ozonation of substrate materials in the Freon system leads tohigher hydroperoxide contents in the substrate materials afterozonation.

EXAMPLE 2 Ozonation of Polysiloxane (Degree of Grafting)

With reference to Example 1, several experiments are carried out to showthe effect of swelling a silicone macromer film in several halocarbons,such as carbon tetrachloride, 1,1,2-trichloro-1,2,2-trifluoroethane(Freon 113) and perfluoro-(1,3-dimethylcyclohexane), prior to ozonatingthereby increasing the hydroperoxidation formation on the surface of thefilm.

One sample of film is placed in a beaker of carbon tetrachloride, asecond film in a beaker of Freon 113 and another sample of film in abeaker of perfluoro-(1,3-dimethylcyclohexane). After each film isequilibrated, ozonization is carried out for five minutes. The films areair dried for 45 minutes. The films are then placed in a graftingsolution which contains 100 grams of deionized water, 1.0 gram ofN,N-dimethylacrylamide, 0.14 gram of methylene-bisacrylamide and 0.3gram of ferrous ammonium sulfate hexahydrate with a continuous nitrogenpurge. After eight minutes, the films are removed from the graftingsolution. The films are distorted, opaque and very lubricious due to thedeep and heavy penetration of the graft.

Polysiloxane films ozonated in water for five minutes and grafted underthe conditions listed above are only marginally lubricious. Said filmsare not highly grafted or distorted as the films ozonated in halocarbonbecause hydroperoxidation is not as great.

EXAMPLE 3 Evaluation of Grafted Polysiloxane Contact Lenses

Polysiloxane contact lenses are ozonated by contact with ozone dissolvedin 1,1,2-trichloro-1,2,2-trifluoroethane (Freon TF or 113) for 15minutes at ambient temperature. The ozonated lenses are then air-driedand placed back into the Freon 113 to swell.

The lenses swollen with the Freon 113 are then placed in a graftingmonomer solution of 1 gram of N,N-dimethylacrylamide, 0.14 gram ofethylene glycol dimethacrylate, 0.1 gram of ferrous ammonium sulfatehexahydrate in 50 grams of water and 50 grams of tert-butyl alcohol.Graft polymerization is carried out for 30 minutes at ambienttemperatures under nitrogen.

The grafted lenses are then removed from the monomer solution, extractedwith water and hydrated with deionized water for testing in the humaneye for general acceptability.

After wearing for 15 minutes on the eye, the grafted polysiloxane lensremained clear and wettable with no protein or lipid depositionobserved.

An ungrafted polysiloxane control lens completely dewets and turnsopaque on contact with the eye after one minute.

EXAMPLE 4 Effect of Graft Composition on Contact Angle

Polysiloxane contact lenses are ozonated and then swollen in Freon 113as described in Example 3. The ozonated and swollen lenses are thenindividually placed in selected grafting solutions are described inExample 3 except that varying amounts of the hydrophobic monomer methylmethacrylate is present in said solutions. Contact angles are measuredon the grafted lenses to ascertain the effect of methyl methacrylatecontent on the hydrophobicity of the grafted lenses.

    ______________________________________                                        Methyl Methacrylate                                                           Content (grams) in                                                                             Contact Angle of                                             the Grafting Solution                                                                          Grafted Lens                                                 ______________________________________                                        0                27                                                           0.1              32                                                           0.2              32                                                           0.4              34                                                           0.8              44                                                           1.0              44                                                           ungrafted lens   80                                                           ______________________________________                                    

Clearly increasing the hydrophobic character of the graft polymer on thepolysiloxane lens surface increases the contact angle and hydrophobicityof the lens appreciably.

EFFECT OF PRESWELLING THE SUBSTRATE WITH A HALOCARBON OR HYDROCARBONAFTER OZONATION, BUT PRIOR TO GRAFTING FOR LIMITING THE GRAFT TO THESURFACE OF THE SUBSTRATE EXAMPLE 5

A silicone macromer film is ozonated in water for five minutes, allowedto air-dry for thirty minutes and is then placed in a beaker ofdeionized water with a nitrogen purge for 15 minutes. The film is thenplace in a grafting solution which is 100 grams of deionized water, 1.0gram of N,N-dimethylacrylamide, 0.14 gram of methylene-bisacrylamide and0.3 gram of ferrous ammonium sulfate hexahydrate. The film is kept inthe grafting solution for 15 minutes under nitrogen before removal andevaluation. The film is found to be very lubricious, but is opaque anddistorted due to deep penetration of the graft into the substrate film.

EXAMPLE 6

The effect of preswelling a substrate with a halocarbon or hydrocarbonprior to grafting to limit the grafting to the surface of the sample isshown in this example.

Polysiloxane contact lenses are ozonated in water for five minutes atambient temperatures. The lenses are then air-dried for 30 minutesbefore being placed respectively into beakers of carbon tetrachloride,hexane, 1,1,2-trichloro-1,2,2-trifluoroethane (Freon 113) orperfluoro-(1,3-dimethylcyclohexane). Each beaker is purged with nitrogenand the lenses are kept submerged for 15 minutes.

The swollen lenses are then placed in a grafting solution made up of 100grams of deionized water, 1.0 gram of N,N-dimethylacrylamide, 0.14 gramof methylene-bisacrylamide and 0.3 gram of ferrous ammonium sulfatehexahydrate. Grafting is carried out under a continuous nitrogen purgefor 15 minutes.

The grafted lenses are found to be clear, lubricious and undistortedsince grafting of the hydrophilic polymer is limited to the surface ofthe polysiloxane contact lenses.

This is in contrast to the grafted film prepared in Example 5 which isopaque and distorted due to graft penetration.

EXAMPLE 7 Contact Lens Modification

Polysiloxane contact lenses are treated with ozone in air for one minuteto ozonate the surface thereof. The lenses are then air-dried and placedin 1,1,2-trichloro1,2,2-trifluoroethane (Freon TF or 113) to saturateand swell said lenses.

The lenses are then placed under nitrogen in a solution of 1 gram ofN,N-dimethylacrylamide, 0.14 gram of methylene-bisacrylamide and 0.3gram of ferrous ammonium sulfate hexahydrate in 100 ml of water. Graftpolymerization is carried out for 15 minutes at room temperature.

The lenses are then extracted with water. The properties of the graftedlenses and of an ungrafted control are seen in the table below.

    ______________________________________                                                        Ungrafted                                                                             Grafted                                               ______________________________________                                        Lens thickness (microns)                                                                        104       102                                               Oxygen Flux*      0.65      0.66                                              Oxygen Permeability**                                                                           76.6      72.8                                              Contact Angle                                                                 Advancing         94        25                                                Receding          51        25                                                ______________________________________                                         *Oxygen Flux in μl O.sub.2 /cm.sup.2 min                                   **Oxygen Permeability O.sub.2Dk = cm.sup.3 (STP) × cm/cm.sup.2          × seccm Hg                                                         

EFFECT OF A CHAIN TRANSFER AGENT DURING OZONATION FOR LIMITING THE GRAFTTO THE SURFACE OF THE SUBSTRATE EXAMPLE 8

A silicone macromer film is ozonated in water for five minutes atambient temperature, allowed to air-dry for thirty minutes, and then isplaced in a beaker of deionized water with a nitrogen purge for 15minutes. The film is then placed in a grafting solution which is made upof 100 grams of deionized water, 1.0 gram of N,N-dimethylacrylamide,0.14 gram of methylene-bisacrylamide, and 0.3 gram of ferrous ammoniumsulfate hexahydrate. Grafting is carried out over a 15-minute periodunder a nitrogen purge. The grafted film is very lubricious, but is alsoopaque and distorted due to the deep penetration of the graftingmaterial into the substrate film.

EXAMPLE 9

A siloxane macromer film equilibrated in an aqueous 10% isopropanolsolution (90 grams of water and 10 grams of isopropyl alcohol) is dippedinto a beaker of deionized water for five seconds, is then placed into acylinder containing perfluoro-(1,3-dimethylcyclohexane) and ozonated forfive minutes. After air drying for thirty minutes, the film is placed ina beaker of deionized water with a nitrogen purge for 15 minutes beforebeing placed in a grafting solution which is made up of 100 grams ofdeionized water, 1.0 gram of N,N-dimethylacrylamide, 0.14 gram ofmethylene-bisacrylamide and 0.3 gram of ferrous ammonium sulfatehexahydrate.

Grafting is carried out under nitrogen for 15 minutes. The film is thenremoved and evaluated. The grafted film is clear, lubricious andundistorted since the grafting has been limited to the surface of thesubstrate due to the chain transfer characteristics of the aqueousisopropanol system.

This is in contrast to the grafted film prepared in Example 8 which isopaque and distorted due to graft penetration.

EXAMPLE 10

An experiment to show the effect of the chain transfer agent onsubsequent grafting is carried out following the general procedure givenin Example 9 except that the amount of time the equilibrated siliconemacromer film is dipped in water is reduced from five (5) seconds tothree (3) seconds.

After the grafting step is completed, the film is not as lubricious asthe film obtain in Example 9.

It is clear that the amount of chain transfer agent (isopropanol in thiscase) present in the equilibrated substrate film is determinative of theamount of subsequent grafting which can take place. In this case thereis more isopropanol present, and consequently less grafting takes place.

EXAMPLE 11

The effect of the amount of chain transfer agent present has on theamount of subsequent grafting is also demonstrated when the procedure ofExample 9 is exactly repeated except for the concentration of theaqueous 50% isopropanol solution (50 grams of water and 50 grams ofisopropyl alcohol) used to equilibrate the siloxane macromer film.

After the grafting step is completed, the film is not as lubricious asthe film obtained in Example 9 again showing that that an increasedamount of chain transfer agent (isopropanol in this case) present in theequilibrated substrate reduces the amount of subsequent grafting whichcan occur.

EXAMPLE 12

A silicone macromer film is placed in an aqueous 10% isopropanolsolution (90 grams of water and 10 grams of isopropyl alcohol) andozonated for five minutes at ambient temperature. After air-drying for15 minutes, the film is placed in a beaker of water with a nitrogenpurge for 15 minutes. It is then placed in a grafting solution of 100grams deionized water, 1.0 gram N,N-dimethylacrylamide, 0.14 gram ofmethylene-bisacrylamide and 0.3 gram of ferrous ammonium sulfatehexahydrate for thirty minutes.

After this time the film is removed and found to be clear and ungraftedtotally unlike the grafted film of Example 8 which is very lubricious,opaque and distorted.

The only difference between the procedures of Example 8 and of Example12 is the presence of an excess amount of chain transfer agent(isopropanol) in this Example which prevents any grafting fromoccurring.

EXAMPLE 13

A polysiloxane-polyurethane film is equilibrated in isopropyl alcoholand then ozonated for ten minutes in perfluoro-(1,3-dimethylcyclohexane)at ambient temperature.

A control film, not first equilibrated in isopropanol, is also ozonatedfor ten minutes in perfluoro-(1,3-dimethylc yclohexane) at ambienttemperature.

Each ozonated film is then placed in a beaker of water. The filmequilibrated with isopropanol remains clear while the control film, notequilibrated with isopropanol, becomes very opaque.

Polar hydroperoxide groups form in the ozonated control film allowingfor the water uptake which leads to opacity.

In the ozonated film, first equilibrated with isopropanol, hydroperoxygroups are not present since the chain transfer agent (isopropanol)prevents their formation by transfer of a hydrogen atom to the freeradical produced on the film during ozonization. Thus, the film isprotected from hydroperoxide formation and film clarity is preserved.

What is claimed is:
 1. A process for modifying the surfacecharacteristics of a preformed polymer substrate to impart alteredproperties in respect to hydrophilicity, hydrophobicity, optics,transmissibility, dyeability or tintability, opacity, diffractability,wettability, bonding characertistics, oxygen permeability, lubricity,diffusibility or bactericidal properties thereto by graft polymerizationon said substrate, having peroxy and hydroperoxy groups on said polymer,of an ethylenically unsaturated monomer, which comprisescontacting thepolymer substrate with a solution which is or contains a chain transferagent to saturate or swell said polymer, said solution being insolublein the perhalogenated liquid medium used subsequently during theozonation step, to limit subsequent hydroperoxidation and peroxidationto the surface of said polymer, ozonating the saturated or swollenpolymer with ozone dissolved in a perhalogenated liquid medium insolublein the solution containing the chain transfer agent, and then graftpolymerizing an ethylenically unsaturated monomer onto essentially onlythe surface of the polymer substrate.
 2. A process according to claim 1wherein the chain transfer agent is a primary or secondary alkanol of 1to 4 carbon atoms.
 3. A process according to claim 2 wherein the chaintransfer agent is dissolved in water or in an aqueous solutioncontaining tert-butyl alcohol.
 4. A process according to claim 2 whereinthe chain transfer agent is isopropanol.
 5. A process according to claim2 wherein the perhalogenated liquid medium is carbon tetrachloride,1,1,2-trichloro-1,2,2-trifluoroethane, perfluorohexane orperfluoro-(1,3-dimethylcyclohexane).
 6. A process according to claim 5wherein the perhalogenated liquid medium isperfluoro-(1,3-dimethylcyclohexane).
 7. A process according to claim 1wherein the graft polymerizing step is carried out in the presence of avariable metal ion to suppress homopolymerization during grafting of theethylenically unsaturated monomer.
 8. A process according to claim 7wherein the metal ion is ferrous.
 9. A process according to claim 1wherein the polymer substrate is a contact lens.